This invention relates to cutoff mechanism for a wire coiling machine.
Coiling machines employed to continuously form fine wire into wire coil, as for electrical resistance elements, typically have employed a flying cutter blade to repeatedly sever segments from the forming coil. Although these have been in various forms, basically the concept involved was to first shift the cutting edge into light engagement with the coil turns for indexing, and then further shifting the blade to sever the indexed coil segment. In performing this operation, a key factor was to minimize damage to the coil and achieve a clean cut with minimal cross sectional area on the severed ends of the wire.
Several years ago, the inventor herein developed an improved cutoff mechanism which allowed the cutter to mechanically index with a lightly powered shift of the blade against the coil at the face of the die, followed by wire cutoff with a highly powered further shift of the blade across the coil. This apparatus, set forth in U.S. Pat. No. 3,370,495, performed considerably better than prior devices, such that the sensitive index allowed cleaner cutoff in many instances.
In modern production practice, however, the nature of the coil diameter, the wire diameter, and the coiling speeds employed are such that the complexities caused by attempting to index the wire with known apparatus, even that in the above noted patent, are too great. The indexing mechanism sometimes does not meet and usually does not hold the required sensitivity, causing a constant problem for maintenance personnel. If the pressure is not quite enough, proper indexing is not achieved. If the blade, in its indexing shift, moves even 0.001 or 0.002 of an inch too much, too much pressure is brought to bear on the delicate, fast-moving coil which is pushed against the side of the die opposite the blade, causing the coil to slow down and swell at this area, thereby rendering the coil useless. It is also desirable to attain and maintain accurate and sensitive indexing for only a very short time interval of blade engagement with the coil. If the blade is retained in indexing engagement for longer time intervals, the rotational speed of the spinning coil is retarded at the blade and die, again causing the coil diameter in this area to swell, thereby rendering the coil useless for uniform electrical resistance as in appliances. I.e., the coil portion is then scrap.
Since maintenance personnel are often unable to maintain necessary cutter index sensitivity, the prevailing practice is to forego attempts to index altogether. Instead, the machine is set to simply chop off the wire without indexing, hoping that the wire will be clean-cut. This, however, requires subsequent visual inspection of the individual coil ends, and hand nipping of many of them to a clean-cut condition.
To fully realize the problem the industry has in obtaining clean-cut coil ends, it should be understood that well over half of all production is so-called close or tight coiled, which is the most difficult form for accurate indexing and clean cutting. One technique which is employed to assist in this operation is to cause the cutter die to be made with the hole through the die at the same angle as the index angle of the coil turns, so that the cutter blade "sees" the coil as nearly parallel turns of wire. This improves the odds of the blade entering the coil between turns, to cause a cleaner cut. However, the results are still far from satisfactory and require subsequent visual inspection and manual trimming of the individual segments.